The anodizing of metals and metal alloys is a well-known process. In this process, a material made of an anodizable metal or an anodizable metal alloy is used as the anode in an electrolytic cell, which moreover comprises a cathode (usually made of noble metal) connected to the anode and an electrolyte having a suitable oxidizing agent. The surface of the metal or of the metal alloy is oxidized when a voltage is applied. In electrolytes that, moreover, contain a suitable concentration of an addition that dissolves the metal oxide again, the method can be carried out under suitable conditions in such a way that a smaller portion of the oxidized surface continues to be dissolved out by the electrolyte, while a larger portion of the surface continues to be oxidized. In this way, structures having micrometer or nanometer dimensions can be created on the oxidized surface, which in the special case of titanium are present in the form of nanotubes.
In many cases, however, these surfaces comprise regions that have no nanostructures after anodizing.